This invention relates generally to the fabrication of integrated circuits.
Transistors utilized in logic circuits have a current drive that is proportional to the mobility of charge carriers. Current drive is related to speed. Thus, it is desirable to improve the mobility of charge carriers.
It is known to use strained channel epitaxial source/drain transistors for the p-channel transistors. The source and drain are formed by ion implantation. The implanted source/drain is then removed using an etching process. A germanium doped silicon material is then selectively deposited into the source/drain regions.
Because germanium expands as it becomes epitaxial, it compresses the channel between source and drain, increasing the mobility of the charge carriers through the channel. However, the need for selective deposition of the epitaxial source/drain raises yield concerns.
Thus, it would be desirable to have alternate ways to form strained channel epitaxial source/drain transistors.